fix(chat): continue external-writer conversations through desktop owner

[ZyPulse-zy]

Opening a thread that is already held by Codex Desktop currently fails with RPC -32600: ... already has an active writer. This change lets Android view the original conversation and, when an optional Desktop companion is configured, send text through its existing owner without creating a fork.

Changes

• Fall back only for the active-writer conflict from thread/resume; read metadata and paginated turns/items without taking ownership. Other RPC failures still surface, and refresh/reconnect restores normal editing when the writer is released.
• Add an explicit external-writer state, independent of the sub-agent input policy. Keep history and explicit Fork available, preserve drafts, and guard Shell, approvals, queues and conversation settings in both the UI and repository.
• Refresh external history while the chat is in the foreground. Preserve loaded/in-flight/failed turn details against the actual server summary, fixing repeated processing-detail reloads when full history contains commentary omitted from the summary. Refresh the newest turn's details directly.
• Add an optional authenticated Python companion that forwards normal app-server traffic and routes text-only sends through the Desktop owner. Delivery is attempted once, inherits Desktop settings and confirms the original thread/message IDs. Clarify the separate “fork into a new conversation” action.
• Add focused repository/API/sync/cache tests and companion unit/integration tests. Configure Mockito as an explicit test JVM agent.

Validation

• :app:lintDebug :app:testDebugUnitTest :app:assembleDebug passed locally with JDK 21 / Android SDK 37: 527 tests, 93 classes, no failures; lint has 0 errors and 26 warnings. JDK 26 validation is left to the repository CI.
• Companion suite: 10/10 passed, including two isolated real CLI app-servers and a mocked Desktop IPC router; the message persists in the original thread without a mobile-side turn/start or thread/fork.
• Codex CLI 0.159.2 recorded and experimental JSON Schema exported under /tmp; reference Codex/Desktop repositories were read only.
• A dedicated real Desktop test received and answered a companion-delivered message in the same thread. Mobile same-thread sending was also confirmed by the user. The newest APK's processing-detail fix has not yet had phone UI verification.

Scope and limitations

The companion is optional and experimental. Its codexAndroid/desktop/* methods are application extensions; Desktop owner discovery/follower IPC is private and version-dependent, separate from the CLI Schema. The current adapter supports Unix sockets, with Linux peer checks; Windows named pipes and macOS have not been validated. Cross-Desktop attachments, queue/steer/interrupt, Shell and approval control are not exposed. A CLI/TUI writer or unavailable companion remains read only, with explicit Fork still available.

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